import java.util.Random;

public class demo1 {
    public static void main(String[] args) {
         char[] ch = new char[52];

        for (int i = 0; i < ch.length; i++) {
            if(i<=25){
                ch[i] = (char)(97+i);
            }else {
                ch[i] = (char)(65+i-26);
            }
        }

        String result = "";
        Random r = new Random();
        for (int i = 0; i < 4; i++) {
            int index = r.nextInt(ch.length);
            result += ch[index];
        }

        int number = r.nextInt(10);
        result += number;
        System.out.println(result);

    }
}
